The objective of this research was to investigate the potential of waste biomass residue as reinforcement for polymers to produce composites as an alternative to synthetic fillers. Bio nanocomposites were produced using Sammaz-14 variety maize cobs Nano cellulose (MC-NF)/High Density Polyethylene (HDPE) / high-density polyethylene grafted maleic anhydride (HD-g-MAH) / organic montmorillonite (Org-MMT). The nanocomposites were compounded with a two-roll mill and fabricated using the injection molding machine. The mechanical (Tensile strength, tensile modulus, and Flexural strength, Flexural modulus), as well as morphological (FE-SEM) properties of the biocomposites, were investigated. The effect of the addition of 1-5% of MC-NF with 2 wt % of Org-MMT and 3% maleic anhydride grafted polyethylene in HDPE were studied, From the results, 2% of OrgMMT was enough to improve the exfoliation and dispersion of the filler in the matrix and 3% incorporation of HD-g-MAH increased the adhesion and reduce the surface tension between the fiber and matrix. hence, creating excellent interfacial adhesion within the composite’s structures, the tensile strength and modulus increased from 19.18 MPa for pure HDPE to 20.24 Mpa (5.5%) at 5 % MC-NF filler loading and stiffness (modulus of elasticity) increased up 52%. Flexural strength and modulus increased from 15.57Mpa for pure HDPE to 17.99 MPa (18.60%) at 5% filler loading and Flexural modulus also increased from 1.99MPa to 2.27MPa (14.07%). The addition of MC-NF improves the mechanical properties up 3% after which the strength starts declining but stiffness steadily increased up to 5% filler loading.